On Sunday, California did something extraordinary: it took the Internet back in time, restoring Obama-era rules that require open access to the Web in defiance of the Trump White House and the Federal Communications Commission. Other states—including Washington, Oregon, and Vermont—have enacted their own net-neutrality rules in the year since the Trump administration eliminated them, but California chose to flout the F.C.C. in the most blatant of ways, not only reinstating Obama’s rules, but banning providers from offering free data on specific apps. Data caps and throttling would effectively be curbed for all customers in California.

Shortly after Governor Jerry Brown signed the bill into law, the Department of Justice slapped the state with a lawsuit. “The Justice Department should not have to spend valuable time and resources to file this suit today, but we have a duty to defend the prerogatives of the federal government and protect our Constitutional order,” Attorney General Jeff Sessions said in a statement on Sunday, calling the law “extreme” and “illegal.” The suit was applauded by F.C.C. chairman Ajit Pai, the architect of the White House’s net-neutrality agenda, who earlier this month criticized the measure as “anti-consumer,” “illegal,” “egregious,” and “radical.” Pai also claimed the new law would hurt consumers. “The law prohibits many free-data plans, which allow consumers to stream video, music, and the like exempt from any data limits,” he said in a statement.

At issue is whether statewide net-neutrality laws are legally viable. Proponents of the California law say the F.C.C. has no power to interfere in state legislation, and at least one expert agrees: “An agency that has no power to regulate has no power to preempt the states, according to case law,” Barbara van Schewick, a law professor at Stanford Law School, told CNN. “When the F.C.C. repealed the 2015 Open Internet Order, it said it had no power to regulate broadband Internet access providers. That means the F.C.C. cannot prevent the states from adopting net-neutrality protections because the F.C.C.’s repeal order removed its authority to adopt such protections.”

Hanging over the administration’s legal contretemps with California is Donald Trump’s own personal war with Silicon Valley. Last month, after the president cited a partisan study on Twitter that suggested Google’s search results were biased against him, Sessions announced he would meet with several state attorneys general to “discuss a growing concern that [tech] companies may be hurting competition and intentionally stifling the free exchange of ideas on their platforms.” The D.O.J. suit against California is a far more concrete threat than the meeting, which experts dismissed as groundless saber-rattling at the behest of a furious president. But it is unlikely to be a political winner. While Trump’s base has been animated by the bias controversy, the vast majority of voters say they favor Obama-era net-neutrality rules.

Still, any attack on California will surely be welcomed by many on the right, who always find reason to take issue with the liberal state’s militantly progressive stances, whether on clean energy (Governor Brown recently signed a renewable energy bill that is seen as a rebuke of Trump) or immigration (the state maintains a sanctuary law that shields undocumented immigrants). The party of states rights, after all, has always drawn the line at positions it opposes.